1. Field of the Invention
The invention relates to apparatus and methods for drilling lateral boreholes from a main wellbore using a high pressure jetting hose for hydrocarbon recovery. In one of its aspects, the invention relates to a method and system for controlling the rate at which a lateral bore hole is drilled by jetting a fluid at high pressure into the formation. In another of its aspects, the invention relates to a method and system for conveying a high pressure jetting hose into a main well bore for later drilling into a producing formation.
2. Description of Related Art
The creation of lateral (also known as “radial”) boreholes in oil and gas wells using high pressure radial jetting was first introduced in the 1980's. Various tools have been used to create a lateral borehole for the purpose of extending the “reach” of the wellbore. The most currently accepted approach involves milling holes in the wellbore casing, and then subsequently using a tubing string to lower a high pressure jetting hose with a nozzle on the leading end into the reservoir. The configuration of the nozzle is such that it contains more opening area in the rearward facing direction than the forward direction. This configuration results in a forward thrust on the nozzle, causing the nozzle to pull the hose behind it as the lateral borehole is created. The upper end of the more-flexible jetting hose is affixed to the lower end of the less-flexible tubing string, and it is therefore desirable to continue feeding the tubing string into the wellbore at the same speed at which the jetting nozzle is creating a lateral borehole. If the tubing string feed rate is too fast, the jetting nozzle path becomes erratic and the lateral borehole is not straight, too slow and the jetting nozzle creates a cavity behind itself resulting in the loss of forward thrust.
Historically, small diameter coiled tubing of ½″ (inch) or less is used to convey the jetting hose, which is typically ¼″ (inch) high-pressure hydraulic hose attached to the end of the small diameter coiled tubing. This small diameter tubing possesses sufficient sensitivity and flexibility to allow the operator some control over the feed-in rate from the surface. The operator uses surface gauges to compare the hanging weight of the relatively lightweight (for example, 4 ft/lb) small diameter tubing to the pressure drop at the jetting nozzle, and typical sensitivity of 25-lbs is generally available.
The prior approach using small diameter flexible coiled tubing is limited, however, in terms of depth, downhole inclination angles, utilization in flowing wells, and other areas. The limited strength of the tubing limits the depths at which it can be used. The angle of the wellbore across which the small diameter jetting hose can be used is limited by the hose's attachment to the end of the small diameter coiled tubing which, although more flexible than standard size coiled tubing, is limited to wellbore angles of around 30 degrees or less. Specialized tube feeding units are required on the surface for the lateral jetting operation, since standard size coiled tube feeding units cannot be used with the small diameter tubing.
Other problems are created by the limitations of the small diameter flexible jetting hose itself that preclude it from being used without tubing to convey it downhole. Small diameter flexible hose is limited in strength and cannot withstand significant tensile forces acting upon it, and is also limited in the length of flexible hose that can be lowered into a deviated main wellbore. Small diameter flexible hose cannot be sealed around the outside of the hose at a grease injector to allow it to be used in conjunction with pressure seal equipment on the surface, thus precluding its use in flowing wells. Small diameter flexible hose cannot be used in conjunction with an injector head on the surface that creates force to push the hose into, or, alternately, pull the hose out of, an oil or gas well, since the hose is so flexible that it cannot be easily pushed downward. Small diameter flexible jetting hose is limited in the deviation angle across which it can be lowered at the bottom of the wellbore.
Still another problem with prior apparatus and methods used to form lateral boreholes with a jetting hose lowered with small diameter coiled tubing is that success is greatly dependent on the skill of the operator in charge of the installation.
Standard size coiled tubing, generally constructed from carbon or stainless steel and deformably wrapped on a powerful reel on the surface, is typically on the order of 1¼″ to 1½″ (inches) in diameter or larger, and weighs significantly more (for example, 2 lbs/ft) than the small diameter coiled tubing used in the prior art. Using standard sized coiled tubing would allow the jetting hose to be employed at greater depths, higher inclination angles, and in flowing well applications, but would make it significantly more difficult to control the tubing feed rate relative to jetting nozzle progress during lateral borehole formation using standard weight versus pressure comparisons. For example, the weight gauges for standard coiled tubing are typically in 100-lb to 200-lb increments, and so are simply not sensitive enough to use the hanging weight of the tubing as a benchmark for comparison to the feed-in rate and pressure drop. Accordingly, even a skilled operator would find it impractical to use the usual weight measurements to control the feed-in rate of the jetting hose using standard coiled tubing.
Standard coiled tubing is also limited in the bending radius that it can traverse, which does not allow its use for some jetting operations.
Thus the use of standard coiled tubing and other larger-diameter, stronger, deep-application hose-conveying equivalents (such as jointed pipe with threaded connections on either end) is discouraged. Conventional jointed pipe also requires a significant amount of time to connect the joints together, which is particularly worrisome when inserting and removing the pipe sections from a well drilled for producing hydrocarbons, since it results in great operating expense due to costs related to labor, rig rental, and other factors known to those skilled in the art.